This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. P22 head-tail connector (also known as portal proteins) is an oligomeric cone-shaped protein that connects the capsid to the tail of bacteriophage P22. The portal protein is also an integral component of the machinery that pumps DNA into the phage head. Each subunit of the oligomer has approximately 85.9KDa and the oligomer is expected to have a 12-fold rotational symmetry with overall size of ~1.1MDa. We have obtained crystals of the P22 head-tail connector under various conditions and tested cryogenic conditions on a rotating anode x-ray generator. The crystals have an average size of ~150*50*50 [unreadable]m3 and a perfect rectangular morphology. We hope to collect a high resolution data set and to determine the structure of the complex by using a cryo-EM low resolution electron density map as a starting model.